1. Field of the Invention
The present invention relates to a roller burnishing apparatus, and particularly to an apparatus for burnishing an object by biasing and pressing a burnishing roller against the object.
2. Description of Related Art
As disclosed in JP-A-2000-52244, for instance, a burnishing roller is biased by a biasing force of a plurality of disc springs and pressed against a workpiece or an object to be burnished. That is, in a roller burnishing apparatus disclosed in the above-mentioned publication, a shaft portion of a roller holder is fitted in a fitting hole formed in a mainbody of a roller burnishing tool such that the shaft portion is axially movable relative to the mainbody, and the burnishing roller is rotatably held by the roller holder. The disc springs are arranged in a row along an axis of the shaft portion, between the shaft portion and a spring retainer (or a spring bearing) that is fitted in the fitting hole such that the spring retainer is axially movable relative to the mainbody. The spring retainer is held in contact with an adjust screw engaged with a portion of the mainbody constituting a bottom portion of the fitting hole. An initial load of the disc springs is adjusted by changing an amount of engagement of the adjust screw with the bottom portion of the fitting hole, so as to adjust a pressing force with which the burnishing roller is pressed against the object, which force is based on the biasing force of the disc springs.
However, after the pressing force with which the burnishing roller is pressed against the object is adjusted, and as burnishing of the object progresses, the pressing force may decrease because of deterioration of the disc springs. The decrease in the pressing force may result in a product of poor quality.